FADEC might be the temporary saviour of traditional engines, but as I see it, there will be a day where the oil companies simply refuse to manufacture a fuel that sells in miniscule volumes compared to Jet A and even automotive fuels. On top of that you need special distribution systems. I can see Avgas being priced out of the market in my life time.
In many countries you cannot get Avgas at any price. In that regard I think diesels are the only way forward. Aerodiesels are still in their infancy today, but I believe given enough time and money the problems will be resolved. They simply have to be.